Several types of centrifugal machines are known in which a frusto-conical, upwardly flaring, filter rotates about a vertical axis. The solid-liquid mixture is discharged at the bottom of the filter, the liquid is filtered out and the solids move upwardly under centrifugal force to be discharged at the top larger diameter rim of the filter; examples of such a system are described in U.S. Pat. No. 2,802,574, dated Aug. 13, 1957, inventor E. Schweppe, entitled "Centrifugal machine for extracting solids from liquids", in U.S. Pat. No. 3,283,910, dated Nov. 8, 1966, entitled "Centrifugal basket", inventors, W. Grieselhuber & al. In the above machines and others known to applicant, there is no system to control the degree of humidity of the solids discharged from the machine.